1. Field of the Invention
This invention relates generally to superabrasive inserts or compacts for abrasive cutting of rock and other hard materials. More particularly, the invention pertains to methods for manufacturing polycrystalline diamond compact (PDC) cutting elements with internal chambers or passages, such cutting elements being mountable on earth-boring drill bits and the like.
2. State of the Art
Drill bits for oil field drilling, mining and other uses typically comprise a metal body into which replaceable cutting elements are incorporated. Such cutting elements, also known in the art (depending on their intended use) as inserts, compacts, buttons, cutters and cutting tools, are typically manufactured by forming a hard abrasive layer on the tip of a sintered carbide substrate. As an example, polycrystalline diamond may be sintered onto the surface of a cemented carbide substrate under high temperature and pressure, typically about 1450–1600° C. and about 50–70 kilobar. During this process, a metal sintering aid such as cobalt may be premixed with the powdered diamond or swept from the substrate into the diamond to form a bonding matrix at the interface between the diamond and substrate. The process is conducted in a high-pressure press receptacle or cell and is commonly known as a high-temperature, high-pressure (HTHP) process.
During drilling operations, cutters are subjected to high temperatures and very high forces imparted upon the cutters in various directions, leading to rapid fracture, delamination, or spalling of the superabrasive table and the underlying substrate.
The introduction of drilling fluids at the cutting end, or face, of the drill bit has long been known as advantageous for cooling the drill bit and washing out formation chips and rock particles from the cutting area. The drilling fluids are typically passed through the tubular drill string and into the bit body itself, which has outlets for discharging the drilling fluid at its cutting end. However, such an arrangement is not always sufficient to maintain the cutting elements themselves at a desired reduced temperature for prolonging their life.
U.S. Pat. No. 5,435,403 of Tibbitts discloses cutting elements formed of a superabrasive material mounted on a substrate. Various interfacial configurations are taught.
U.S. Pat. Nos. 5,316,095 of Tibbitts and 5,590,729 of Cooley et al., both assigned to the assignee hereof, Baker Hughes Incorporated, and hereby incorporated by reference herein, disclose cutting elements which have internal chambers and/or passages within the substrates thereof. These chambers and passages serve for passing drilling fluid to directly cool the diamond tables as well as for flushing cutting-induced chips of formation or other drilling-produced solids from the cutting surfaces engaging the formation. The internal chambers and/or passages are formed either during the formation of the substrate, or by machining, drilling, or other procedures subsequent to the construction of the substrate but before attachment of the superabrasive table thereto. The superabrasive table and substrate are usually bonded together by using a known HTHP process. As shown in these references, many different variations in cutting element types, sizes, shapes, and passage configurations are possible.
While the internally cooled cutting element is conceptually advantageous from a longevity standpoint, its construction has been difficult and time consuming, with all too frequently occurring problems arising in the HTHP bonding process. A primary problem is that during the HTHP process for bonding of the superabrasive, typically a diamond containing, table to the substrate, the substrate material, typically a carbide such as tungsten carbide, can yield under pressure and be forced into preformed passage(s) in the substrate, thereby constricting or even wholly blocking the preformed passage(s). In some cases, the substrate may collapse and even break, ruining the cutting element. In addition, diamond particles also may be forced into the preformed passage(s), closing off some as well as decreasing the diamond table thickness and integrity. In order to maintain an open passage for the flow of drilling fluid, the intrusive material, e.g., very hard carbide or diamond material, must be mechanically removed. Effective removal is difficult and costly, if not impossible, and the resulting cutting element may not be as structurally strong as an element having had no carbide and/or diamond material in the internal passage or cavity.
Forming a non-linear or complex-shaped passage or cavity, or passages or cavities, in a suitable location in a substrate following bonding to a superabrasive table is very difficult, inasmuch as precise drilling/machining of the very hard carbide of the substrate in different directions is generally required, and the attached superabrasive table may block access for drilling the interior of the substrate in the required directions.
A satisfactory method is needed for fabricating cutting elements with internal substrate passages with a high degree of reproducibility and reliability while significantly reducing the cost of manufacture, inasmuch as the present manufacturing methods are inadequate in that regard.